Latch-Based Level Shifter for Balanced Duty Cycle Transitions
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Solution Overview
Problem
High-speed digital receivers face stringent duty-cycle distortion requirements due to unmatched rise/fall transitions in existing level shifters, leading to jitter and data errors in high-speed digital communication applications.
Innovation Solution
A latch-based level shifter with a capacitor and field effect transistors balances rise and fall times of differential logic signals, using capacitive coupling to stabilize the latch and ensure symmetric transitions, thereby eliminating timing variances between input and output signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If simple level shifters are used to translate logic levels, then level translation is achieved, but duty cycle distortion occurs due to unmatched rise/fall transitions
Solution Approach 1:
The patent applies asymmetry by using different capacitor values (C1 and C2) for balancing rise and fall transitions. The first capacitor is coupled to the first input node and the second capacitor is coupled to the second input node, allowing independent adjustment of rise time and fall time to achieve symmetric overall performance despite asymmetric individual components
Solution Approach 2:
The patent changes the electrical parameters by introducing capacitors in parallel with the transfer elements. This modifies the time constants of the circuit by adding capacitive reactance, thereby controlling the rise and fall times of the output signal to match the input signal's duty cycle characteristics
2Speed
If conventional level shifters are used in high-speed digital receivers, then level shifting is achieved, but jitter and data errors increase due to timing distortion
Solution Approach 1:
The patent applies preliminary action by pre-balancing the rise and fall transitions through carefully selected capacitor values before the signal proceeds through the rest of the receiver circuitry. This preliminary timing adjustment prevents subsequent jitter and data errors in high-speed operation
3Device complexity
If unmatched rise/fall transitions are present in level shifters, then circuit simplicity is maintained, but timing variance between input and output signals increases
Solution Approach 1:
The patent uses capacitors as intermediary elements between the input nodes and the output nodes. These capacitors mediate the timing characteristics by storing and releasing charge to equalize the rise and fall times, acting as a buffer that reconciles the timing differences without requiring complex circuit reconfiguration
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively reduces jitter and data errors by ensuring balanced signal transitions, meeting stringent tolerance requirements for high-speed digital communication applications, such as USB 2.0 receivers, with duty cycle variations reduced to around 0.5%.
Implementation Method 1
The level transition balancing circuit includes a capacitor in parallel with a transfer element for each of the two input nodes. The capacitor balances the respective rise and fall times during the transition using a capacitance and a previous level shifted version of the complimentary logic level stored in the logic element.
Implementation Method 2
The transfer element includes a field effect transistor (FET).
Implementation Method 3
The logic element includes a latch that further holds the output levels of the level shifted versions of the two complimentary logic levels after the transition. The latch can be embodied as a pair of cross coupled inverters.
Data Source
AI summary
A level shifter and method are provided for balancing a duty cycle of a signal. An input circuit receives a differential logic signal with two complimentary logic levels. A level transition balancing circuit balances the rise and fall times of a level shifted version of each complimentary logic level during a transition from a first to a second of the logic levels and a level shift. A logic element stores and provides outputs of the level shifted versions of the logic levels. The level transition balancing circuit can include a capacitor in parallel with a transfer element for each input. The capacitor destabilizes inputs to the logic element and balances the transition using a capacitance and a level previously stored in the logic element.